Preparation of aromatic carboxylic acid amides



Patented Sept. 16, 1952 PREPARATION OF AROMATIC CARBOXYLIC ACID All/[IDES Marcus A. Naylor, In, Bloomfield, N. J., assignor to E. I. du Pont de Nemours and Company, Wil-- mington, Del., a corporation of Delaware No Drawing. Application ctober 25,:1949, a SerialNo.123,531

1. v invention relates to "the "preparation of aromatic :carboxylic acid amides :from aromatic hydrocarbons under the conditions ofuthe Willagerodt reaction. i

In- 1887 Willgerodt discoveredlthat :aryl "alkyl .ketones' .react atlhigh temperatures and under pressure with yellow ammonium :polysulfide 'to form'crystalline nitrogenous materials. The following year he reported that "these products were amides of the aryl-substituted aliphatic acids containing the same :number of carbon atoms as the starting ketones, accompanied by the arc-.- monium salts of these acids. In subsequent 'years'Willgerodt extendedithe 'reaction'to a large number of different a'ry'l alkyl ketones. Since that time theWillgerodttreaction has been applied toalarge number of other organic .com-

pounds, and up to the present time the following types of compounds are known to react under the conditions of the Willgerodt reaction to give carboxylic acids and derivatives thereof having the'same number of carbonatoms as the :organic compound from which they are formed: dialkyl ketones, aralkyl alkyl ketones, cycloallgyl ketones, alicyclic'ketones, aliphatic'alcohols, aliphatic organic halides, aldehydes, thioaldehydes, olefins, aliphatic and aromatic substituted *olefins, :acetylenes and aliphatic and aromatic ;-sub'- istituted acetylenes.

.Anobject-of the present invention is to e tend the "Willgerodt reaction to m aromatic hydrocarbons. A furtherobje'ct of the present invention-is 'to .provide a method of preparing aromatic carboxylic amides from aromatic hydrocarbons. Other objects willbeapparent-from the description of the invention given hereinafter.

The above objects are accomplished according ,to'the present invention by heating together a monocyclic aromatic hydrocarbon at .least one -.hydrogen atom of the aromatic ring replaced with an alkyl radical, the alkyl radical having" at least one hydrogen atom attached $0 the :carbon atom ialpha to said aromatic 'ring, with a" mixturecomprising essentially sulfur-and ammonia at J'a temperature :between 1180 C. and

7 Claims; (01. 260-55 8) ;Morefspecifically, thepresent inve'ntionzcomprisesheeting-together an aromatic hydrocarbon having the formula, CGHxRy, wherein 1B :is an alkyl radical, the alkyl radical having at least one hydrocarbon atom attached to the carbon 18.0w; andis'aoad In the preferred 'and'still more specific form the present invention comprises heating together an aromatic :hydrocarbon having the formula .CsHsR, wherein R is an .alkyl radical having no more than 4 carbon atoms, the alkylradical hav ing at least one hydrogen atom attached to the carbon atom alpha to'thearomatic ring, with 'a mixture comprising essentially sulfur and aqueous ammonia at a temperature between 240 C. and 300 C. r

The present/invention resides primarilyin'the discovery that aromatic hydrocarbons as characterized above will'reactunder the conditions-oi" the Willgerodtreaction to give aromatic 'carboxylic acid amides. Heretofore, certain unsaturated aromatic hydrocarbons had been converted to corresponding amides butit was not known that the herein considered aromatic "hydrocarbons 'could be converted in "this-manner and,-thus; a practical method of obtaining :certain aromatic acid amides has been-provided where such amides could only be prepared with great difficulty, if atall, heretofore.

The conditions, in general, of the Willgerodt reaction are known and are "applicable "the present invention except that the temperature range herein specified should be observed. That is, the reaction is normally conductedin a closed reagent simply powdered sulfur added to am mania. either aqueous or anhydrous. although it is to be understood that in defining the reagent herein as comprising essentially sulfur and ammonia, the polysu'lfide form of the Willgerodt reagent is included, the present invention in its broader phasenot beingiconcerned Withispecific variations of the Willgerodt. reagent.

The following examples in whichall parts are given by weight unless otherwise specified, .illustrate specific embodiments oftheinvention, l

v 7 Example I The i following' reaction was carried out inla stainless steel hydrogenation bomb equipped with iron gaskets. Agitation of the bomb was 30- com-plished by placing the bomb in 1a ,rockerljas .sem-bly equippedwithband-heaters. l

, i.mixture of 46 parts toluene roisfi on parts of sulfur (2 mols), and 135 parts of concentrated aqueous ammonia (28% ammonia) (2.22 mols) was introduced into the bomb and the mixture was agitated for a period of about four hours at 270 C. The initial pressure was about 1300 lbs/sq. in. and rose to about 1500 lbs/sq. in. About 20 parts of toluene remained unreacted as an upper layer when the bomb was opened.

The toluene layer was evaporated to dryness giving a residue of sulfur and amide. Extraction with water removed 3.9 parts of the amide. The above amide product was combined with 5 parts of amide filtered from the cooled aqueous layer. After several recrystallizations from water and benzene, the amide product was iden- Example II The following reaction was carried out in the same type of bomb used in Example I.

A mixture of 60 parts cumene (isopropyl benzene) (0.5 mol), 64 parts of sulfur (2.0 mols), and 135 parts of concentrated aqueous ammonia (2.22 mols) was introduced into the bomb and the mixture was agitated for a period of two hours at 270 C. The initial pressure was about 1700 lbs/sq. in. and the final pressure was about 3500 lbs/sq. in. When the bomb was opened, a small amount of unreacted cumene was obtained as an upper layer in the product. Crude amide was isolated by filtration from the reaction mixture.

Recrystallization from benzene gave a white solid with a broad melting range. The sample was recrystallized several more times from benzene, and the solid obtained was then recrystallized twice from water and was found to have the following melting point and analysis:

gigggg? Benzamide Melting Point C.) 126-126. 5 125-130 Percent Carbon 68 92-69. 26 69. 35 Percent Hydrogen. 6. 08-6. 19 5.82 Percent Nitrogen ll. 60-11. 70 11. 55

The benzene filtrates from the above recrystallizations yielded a more soluble solid which had the following melting point and analysis:

Reaction PhenylAcetg figg Product amide A cetamide Melting Point C.) 71-74 156-157 91-92 Percent Carbon 70. 60-70. 73 71. 2 72. 4 Percent Hydrogen 7.13-7. 24 6. 67 7. 42

Very little hydrogen sulfide was 15 bined with the solid which was filtered from the solid with a broad melting range of -128 C. Fractional crystallization from the benzene separated the following two materials:

The above results suggest a cleavage of carbon to carbon bonds during the course of the reaction period. Literature dealing with the mechanism of the Willgerodt reaction makes a point of the fact that the subject reaction never rearranges or alters the carbon skeleton. However, prior to the present invention the subject aromatic hydrocarbons had not been subjected to the conditions of the Willgerodt reaction. Whether the carbon to carbon cleavage to give the above products occurs by a stepwise mechanism or results from the formation of several different intermediates is not known. One possible mechanism for the preceding series of products maybe as given in the following equations. It is tobe understood that this approach is purely theoretical and does not alter the facts presented herein.

CH; C O N112 hydrolysis C H H CQHgCH p CH CH;CH3

decarboxylation H3 Hz Cumene Methyl phenyl Ethyl benzene acetamide 1 hydrolysis CaHtCONHz C6H5CH3 CtHsCHzCONH:

decarboxyl Bcnzamide Toluene ation Phenyl acetamide From the results obtained in this example it is evident that the ratios of the yields'of the products obtained can be altered by varying the reaction conditions and the proportions of the reactants. Experience has shown that when a greater proportion of the aromatic hydrocarbon is used, more of the amide of the original starting material is formed and lesser amounts of the degradation products are obtained.

Example III The following reaction was carried out in the same type of bomb used in Example I.

A mixture of 53 parts of ethylbenzene (0.5 mol) 64 parts of sulfur (2 mols), and parts'of concentrated aqueous ammonia (2.22 mols) was introduced into the bomb, and the mixture was agitated for a period of two hours at 260 C. The initial pressure of about 1700 lbs/sq. in. went to about 3300 lbs./sq. in. at the end of the reaction. The solid which crystallized'oncooling the bomb was recrystallized and decol'orized from water. Fractional crystallization from benzene separated two solid materials which were identified as in Example II, as phenyl acetamide and benzamide.

Example IV The following reaction was carried out' in'the same type of bomb used in Example I. f

A mixture of 26 parts of p-xylene-(0.5 m'Ol),

.concentrated .iaqueous :ammoni'a, 1222-2. mols). "was intrcduce diinto the :bomb, and :thermixture :was

.-.agitated .for aperiod'iof, 12%. 111011135 at 26.0? :G.

:Thersolid-whichiormed on .fcooling the bomb was nepartedrfromthe liquorsbyfiltration.

The solid obtained was amorphousriigl tzyellow and; insoluble in boilingcwater. :ltrwasidried over epota'ssium:hydroxideandithen.over.;sulfnric acid. :Thezmaterial was extractedtthree times"withllhot water,- ,and six times with carbon disulfiderrcto 'removersulfur'l. The r.esulting:product-rwasid'entiiied as :terephthalamidemavingza meltingcpoint above :2609: C. and .having .a. nitrogen-analysis 01 The; filtrate 'iromzthe bombzwas :evaporated to dryness cto: :remove :ammoniumrsul'fide, ,1 and the :solid residue: was extracted with hot water. :Th e yellow, amorphous solid r=leitraiter this; treatment was tentatively identified :as a.:mixture. -.ofJ-.:p- :methylbenzamide and benzamide.

It is to be understood :that theioregoing :examples merely illustrated, :and the present :invention broadly comprises :heating together a .monocyclic aromatic hydrocarbonhaving at. least one hydrogen atom of the aromatic ring replaced with an alkyl radicaLthealkyl radical having at least one hydrogen atom attached to the carbon atom alpha to said a'romatic :ringxwith the Will- ,gerodt-reagent, i. e., amixture comprising essentially sulfur and ammonia, ata temperature between 180 C. and 340 C When applied to the-aromatic'hydrocarbons of the present invention, the: Willgerodt ireaction maybe carriedoutunder substantially anhydrous conditions or in the presence of water. When substantially anhydrous conditions prevail, the carboxylic acid derivative resulting is a thioamide. These thioamides contain the group CSNH2. When water is present, the corresponding oxyamide is obtained containing the group --CONH2.

Depending upon the end product desired, the reaction may be carried out in the presence of V maticihydrocarbonsincreases,lower, temperatures should be employed .to. obtain aromaticcarboxyllc .acid amides, having the same number,of carben atoms as i.t he.-particular startingymaterial, -As

thetreactiontemperature is increased,the;severity of degradation of the starting material increases and cleavageof ,carbonto carbon bondsjwillgoccur. Hence, the reaction temperatureselected in any given case will be dependentupon .the;particular inert solvents either in the presence of water or 1 under substantially anhydrous conditions. The use of a suitable solvent such as dioxane, pyridine or benzene may facilitate separation of the 'desired end product from the reaction liquors. Furthermore, such inert solvents may be used to render complex mixtures of reactants homogeneous and reduce the total vapor pressure of the heated reaction mass.

In addition to the aromatic hydrocarbons disclosed in the foregoing examples, the following specific hydrocarbons may be reacted according to the process of the present invention to produce various derivatives of aromatic carboxylic acids, particularly aromatic carboxylic acid amides and thioamides. Included among such aromatic hydrocarbons are (0, m, p-) xylene, triethyl benzene (sym. or unsym.) mesitylene, cymene, n-butyl benzene, isobutyl benzene secondary butyl benzene, hexamethyl benzene, and pentamethyl'benzenefi All of these aromatic hydrocarbons are monocyclic aromatic hydrocarbons having at least one hydrogen atom of the aromatic ring replaced with an alkyl radical, any remaining valences of the aromatic ring being satisfied by hydrogen and the alkyl radical having at least one hydrogen atom attached to the carbon atom alpha to the aromatic ring.

The products resulting from treating the herein described type of aromatic hydrocarbon according to the present process may be one or more of the following: salts of carboxylic acids, having volatility .of .the reactants orthereaction medium.

For the process of the present invention; "ift'giS recommended that a temperature between 180 and 340 C. be used. A preferred temperature range is between 240 C. and 300 C.

The proportion of aromatic hydrocarbon to the Willgerodt reagent may be varied widely. Theoretically, for each mole of aromatic hydrocarbon there should be one mole of ammonia and three moles of sulfur. There is no particular advantage in using more than the theoretical amount of ammonia but an excess does no harm and where the ammonia is added in a concentrated'aqueous solution, as in the examples, an excess may be added for the incidental purpose of having sufficient water present to facilitate removal of the reaction products from the reaction vessel; In the case of the sulfur, an excess above the theoretical amount tends to increase the rate of reaction and will preferably be used even though it is not necessary.

From the foregoing, it will be appreciated that the proportion of Willgerodt reagent is not critical as the reaction will take place in the presence of any appreciable amount of the reagent, merely the rate of the reaction and the approach of the yield to theoretical being affected as proportions are varied. Further, the considerations with respect to proportions are equally applicable whether a mixture of sulfur and ammonia are used or yellow ammonium polysulfide. Actually, even if ammonium polysulfide is not used at the start, hydrogen sulfide is formed in the reaction and that reacts with the ammonia to give am-' monium polysulfide.

As manyapparently widely difierent embodiments of this invention may be made Without departing from the spirit and scope thereof, it is to the. specific embodiments thereof except 'as fined in the appended claims.-

The invention claimed is: v

aromatic hydrocarbon has the formula CGHxRy,

wherein R is an alkyl radical, said alkyl radical having at-leastone hydrogen atom attached to the carbon atom alpha to the romatic ring, a: is an integer ranging from 3 to .5, and y' is an in- "teger ranging from 1 to 3.

3. A process as set forth in claim 1 wherein said aromatic hydrocarbon has the formula CsHsR, wherein R. is an alkyl radical having no more than 4 carbon atoms, said alkyl radical having at least one hydrogen atom attached to the carbon atom alpha to the aromatic ring.

4. A process for preparing aromatic carboxylic acid amides which comprises heating a monocyclic aromatic hydrocarbon having at least one hydrogen atom of the aromatic ring replaced with an alkyl radical, any remaining valences of said aromatic ring being satisfied by hydrogen and said alkyl radical having at least one hydrogen atom attached to the carbon atom alpha to said aromatic ring, with a mixture comprising essentially sulfur and aqueous ammonia, at 240 C.-

' 5.:Aprocess asset forth in claim 4 wherein said aromatic hydrocarbon has the formula CcHzRv, whereinR is an alkyl radical, said alkyl radical having at least one hydrogen atom attached to the carbon atomialpha to the aromatic ring, a: is an integer ranging from 3 to 5, and y' is an integer rangingfrom l to 3.

6. A process as set forth in claim 4 wherein said aromatic hydrocarbon has the formula CsHsR, wherein R is an alkyl radical having no more than 4 carbon atoms, said alkyl radical having at least one hydrogen atom attached to the carbon atom alpha to the aromatic ring.

7. A process for the preparation of aromatic carboxylic acid amides which comprises heating a monocyclic aromatic hydrocarbon having at least one hydrogen atom of the aromatic ring replaced with an alkyl radical and all remaining valences of said ring satisfied by hydrogen and said alkyl radical having at least one hydrogen atom attached to the carbon atom alpha to said aromatic ring, with a mixture of sulfur and aqueous ammonia at an elevated temperature within the range from about 260 C. to below the critical temperature of water, in a closed vessel.

MARCUS A. NAYLOR, J R.

REFERENCES CITED UNITED STATES PATENTS Name Date Carmack et a1 Jan. 24, 1950 Number 

1. A PROCESS FOR PREPARING AROMATIC CARBOXYLIC ACID AMIDES WHICH COMPRISES HEATING A MONOCYCLIC AROMATIC HYDROCARBON HAVING AT LEAST ONE HYDROGEN ATOM OF THE AROMATIC RING REPLACED WITH AN ALKYL RADICAL, ANY REMAINING VALENCES OF SAID AROMATIC RING BEING SATISFIED BY HYDROGEN AND SAID ALKYL RADICAL HAVING AT LEAST ONE HYDROGEN ATOM ATTACHED TO THE CARBON ATOM ALPHA TO SAID AROMATIC RING, WITH A MIXTURE COMPRISING ESSENTIALLY SULFUR AND AMMONIA, AT 180* C.-340* C. 